The long-term clinical effect of valve regurgitation is recognized as a significant contributor to cardiovascular related morbidity and mortality. Thus, for many therapies intended to treat the mitral valve, one primary goal is to significantly reduce or eliminate regurgitation. By eliminating the regurgitation at the mitral valve, the destructive volume overload effects on the left ventricle can be attenuated. The volume overload of mitral regurgitation (MR) relates to the excessive kinetic energy required during isotonic contraction to generate overall stroke volume in an attempt to maintain forward stroke volume and cardiac output. It also relates to the pressure potential energy dissipation of the leaking valve during the most energy-consuming portion of the cardiac cycle, isovolumetric contraction. Additionally, therapies for MR reduction can have the effect of reducing the elevated pressures in the left atrium and pulmonary vasculature reducing pulmonary edema (congestion) and shortness of breath symptomatology. Such therapies for MR reduction may also have a positive effect on the filling profile of the left ventricle (LV) and the restrictive LV physiology that can result with MR. These pathophysiologic issues indicate the potential benefits of MR therapy, but also indicate the complexity of the system and the need for a therapy to focus beyond the MR level or grade.
Some therapies for treating MR may worsen other (non-MR) existing pathologic conditions or create new pathologic conditions. One of the conditions to be managed is mitral stenosis or creation of an inflow gradient. That is, if a prosthetic valve system is used that does not allow for sufficient LV inflow without elevated filling pressures, then some benefits of MR reduction may be dissipated or lost. An additional condition to be managed is left ventricular outflow tract (LVOT) obstruction or creation of high LVOT pressure gradients. That is, if a prosthetic valve system is used that does significantly obstructs the LVOT, then some benefits of MR reduction may be dissipated or lost. Also, if the procedure results in damage to atrial tissue at surgery, it can increase the likelihood of the negative physiologic effect of atrial fibrillation. Further, some prosthetic valve systems may increase the risk of higher LV wall stress through an increase in LV size (LV geometry). Due to the integral relationship of the mitral valve with LV geometry through the papillary and chordal apparatus, LV wall stress levels can be directly affected resulting in alterations of LV filling and contraction mechanics. Accordingly, in some circumstances, a prosthetic valve system that worsens the geometry of the LV can counter the benefits of MR reduction because of the alteration of contractile physiology.